The invention relates to a pulse code modulated (PCM) audio signal transmission system which compensates for signal interference in the PCM signal.
During the transmission of a PCM audio signal, statistically distributed interference occurs which becomes more or less audible during audio playback. When recording a PCM audio signal by means of a magnetic tape recorder, such interference is produced essentially by dropouts on the magnetic tape.
In connection with television signals, it is known to add the signal of the preceding line as a substitute signal during the duration of a dropout. This solution is based on the acceptable assumption that the signals of horizontal lines that are successive in time have essentially the same informational contents. Such a solution is not possible for an audio signal because no correlation exists between audio signal sections of successive time periods.
Circuits are also known with which it is possible to correct and/or cover-up errors occurring during recording in the digital recording or transmission path. Such error correction systems or error cover-up algorithms fail, however, if the interference exceeds a defined time period. For such a case, referred to as a "digital catastrophe", it is known to provide an electronically controlled muting circuit which blanks out the output signal for the duration of an uncorrectable error. Such a muting circuit serves essentially only to protect the subsequent electroacoustic components and the listener's hearing because a digital transmission based on interference could produce output signals of an extremely high amplitude. The actual error cannot be corrected by the muting circuit. Transmission or recording at hi-fi quality can no longer be realized with a temporarily operating muting circuit.